Could fault with speed sensor be through wear and tear or result of a rear end collision.

Ive had a diagnostic machine hooked up to my car, the mechanic said I had a fault with my speed sensor. I was in a collision about three months ago and was hit in the rear at about 15mph. The Insurance (car repair company) fixed the damage and said they checked the gearbox for faults? About a week after receiving my car back from the insurance repair company, I noticed when driving in automatic it would over rev slightly to get into 1st gear. Then about 3-4 weeks after the collision my ABS light, Service light and Check Gearbox message appeared on my dashboard. I can no longer drive in automatic as it wont catch 1st gear, I now have to drive using the gears as my car is semi automatic. Could the fault with the speed sensor be caused from the rear end collision or could this be through wear and tear. Thanks.